Math Problem Statement

Solve the inequality algebraically: (x-7)(x+5)/x ≥ 0.

Solution

The inequality given is:

(x7)(x+5)x0\frac{(x - 7)(x + 5)}{x} \geq 0

Let's solve this algebraically by following these steps:

Step 1: Identify critical points

The expression involves factors (x7)(x - 7), (x+5)(x + 5), and xx. The critical points are the values of xx that make any factor equal to zero:

  1. x=0x = 0 (from the denominator).
  2. x=7x = 7 (from (x7)=0(x - 7) = 0).
  3. x=5x = -5 (from (x+5)=0(x + 5) = 0).

So, the critical points are x=5x = -5, x=0x = 0, and x=7x = 7.

Step 2: Determine the sign in each interval

We now test the sign of the expression in the intervals determined by the critical points: (,5)(- \infty, -5), (5,0)(-5, 0), (0,7)(0, 7), and (7,)(7, \infty).

  • For x(,5)x \in (-\infty, -5): Choose x=6x = -6: (67)(6+5)6=(13)(1)6=136,positive.\frac{(-6 - 7)(-6 + 5)}{-6} = \frac{(-13)(-1)}{-6} = \frac{13}{6}, \quad \text{positive}.

  • For x(5,0)x \in (-5, 0): Choose x=1x = -1: (17)(1+5)1=(8)(4)1=32,positive.\frac{(-1 - 7)(-1 + 5)}{-1} = \frac{(-8)(4)}{-1} = 32, \quad \text{positive}.

  • For x(0,7)x \in (0, 7): Choose x=1x = 1: (17)(1+5)1=(6)(6)1=36,negative.\frac{(1 - 7)(1 + 5)}{1} = \frac{(-6)(6)}{1} = -36, \quad \text{negative}.

  • For x(7,)x \in (7, \infty): Choose x=8x = 8: (87)(8+5)8=(1)(13)8=138,positive.\frac{(8 - 7)(8 + 5)}{8} = \frac{(1)(13)}{8} = \frac{13}{8}, \quad \text{positive}.

Step 3: Analyze the critical points

  • At x=5x = -5, the numerator becomes zero, so (x7)(x+5)x=0\frac{(x - 7)(x + 5)}{x} = 0. This satisfies the inequality.
  • At x=0x = 0, the expression is undefined (division by zero).
  • At x=7x = 7, the numerator becomes zero, so the expression equals zero, satisfying the inequality.

Step 4: Conclusion

The solution to the inequality is where the expression is either positive or zero. Based on the sign analysis and critical points, the solution in interval notation is:

(,5](0,7](-\infty, -5] \cup (0, 7]

Would you like a more detailed explanation on any step or have further questions?

Here are 5 related questions for deeper understanding:

  1. How would the solution change if the inequality were strict (i.e., >0> 0 instead of 0\geq 0)?
  2. What happens if one of the critical points were a repeated root?
  3. How can we visualize this inequality on a number line?
  4. Why is x=0x = 0 excluded from the solution?
  5. How do rational inequalities differ from polynomial inequalities?

Tip: Always check for undefined points in rational inequalities to avoid errors in your solution!

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Math Problem Analysis

Mathematical Concepts

Inequalities
Rational Expressions
Critical Points
Sign Analysis

Formulas

Sign analysis across intervals using critical points
Handling undefined points in rational expressions

Theorems

Zero Product Property
Properties of Rational Inequalities

Suitable Grade Level

Grades 10-12